FEMTOSECOND SOLITON TRANSMISSION CHARACTERISTICS IN AN ULTRALONG ERBIUM-DOPED FIBER AMPLIFIER WITH DIFFERENT PUMPING CONFIGURATIONS

The transmission characteristics of femtosecond optical solitons in an 18.2 km long erbium-doped fiber amplifier have been investigated in details by changing the pumping configuration. With backward pumping, a lossless transmission of 440 fs solitons at 1.55-mu-m has been realized with a pump power of 16 mW. Here the output pulsewidth is determined by the spectrum modified by the solition self-frequency shift. In a bidirectional pumping configuration, 440 fs soliton pulses have been transmitted for a total pump power of 38 mW, where the output pulse width is determined by the original 1.55-mu-m spectrum. Although a femtosecond soliton is very weakly trapped in the EDFA gain bandwidth of 1.55-mu-m and the soliton self-frequency shift inevitably occurs, the femtosecond pulse component still exists at 1.55-mu-m and a pulse can be successfully transmitted with a gain of 11 dB and very little pulse broadening.